A hydrothermal time model explains the cardinal temperatures for seed germination

Published and additional data for polyethylene glycol 8000 (PEG), formerly PEG 6000, solution water potentials (Psi) are compared. Actual bars Psi over the concentration range of 0 to 0.8 gram PEG per gram H(2)O and temperature (T) range of 5 to 40 degrees C are best predicted (probably within +/- 5%) by this equation: Psi = 1.29[PEG](2)T - 140[PEG](2) - 4.0[PEG]. Although transformable through division by [PEG] to virial equation form, results indicate that the coefficients are not virial. Mannitol (MAN) interacts with PEG to produce Psi significantly lower than additive. Vapor pressure osmometer (VPO) data for MAN-PEG synergism compared favorably with those from thermocouple hygrometry; and VPO data showing the interactions between PEG and four salts are presented. The synergism of MAN-PEG and of NaCl-PEG are related linearly to the concentration of solute added with PEG.